The present invention relates to a process for halide-free synthesis of alkali-metal tetraorganylborate compounds.
Tetraorganylborate compounds have a broad spectrum of utility. Tetraalkylborate compounds are used as alkylating agents, polymerization catalysts, and polymer stabilizers. The most widely-reported tetrarylborate, sodium tetraphenylborate, is an important analytical reagent, as well as an NMR chemical shift reagent, a photographic reagent, and a catalyst in several polymerization reactions. Gmelin, Handbuch der Anorganischen Chemie, 33/8, Boron Compounds, (1976) discloses a number of uses for sodium tetraphenylborate, including use as a quantitative precipitant of radioactive cesium from reactor waste effluents.
Wittig et al., U.S. Pat. No. 2,853,525, disclose a process for producing sodium tetraphenylborate by reacting a Grignard reagent with a boron trihalide in accordance with the following two-step reaction: EQU (1) 4C.sub.6 H.sub.5 MgX+BX.sub.3 .revreaction.(C.sub.6 H.sub.5).sub.3 B.C.sub.6 H.sub.5 MgX+3MgX.sub.2 EQU (2) (C.sub.6 H.sub.4).sub.3 B.C.sub.6 H.sub.5 MgX+Na.sup..sym. .revreaction.(C.sub.6 H.sub.5).sub.4 BNa+Mg.sup..sym. X
X in the foregoing formulas is a halide ion.
Washburn et al., U.S. Pat. No. 3,311,662, describe a method of making sodium tetraarylborate compounds, including sodium tetraphenylborate (NaB(Ph).sub.4), by reacting aryl sodium compounds with triarylborons, e.g., EQU ArNa+B(Ar).sub.3 .fwdarw.NaB(Ar).sub.4,
or by reacting aryl sodium compounds with boron trihalides, e.g., EQU 4ArNa+BCl.sub.3 .fwdarw.NaB(Ar).sub.4 +3NaCl.
Ar in the foregoing formulas can be aryl, alkaryl, haloaryl, aryloxyaryl or alkoxyaryl.
Hough et al., J. Am. Chem. Soc. 80: 1828 (1958), disclose the following reaction of gaseous diborane with sodium metal to provide sodium borohydride: EQU 2Na+2B.sub.2 H.sub.6 .fwdarw.NaBH.sub.4 +NaB.sub.3 H.sub.8.
Schlesinger et al., J. Am. Chem. Soc. 75: 199 (1952), disclose a method of preparing sodium borohydride by reacting sodium methoxide or sodium tetramethoxyborohydride with gaseous diborane, e.g.: EQU 3NaOCH.sub.3 +2B.sub.2 H.sub.6 .fwdarw.3NaBH.sub.4 +B(OCH.sub.3).sub.3.
In addition, Schlesinger et al. report that lithium ethoxide (LiOC.sub.2 H.sub.5) reacted with diborane to provide lithium borohydride. However, this reference also reports that potassium methoxide "did not react" with diborane to produce potassium borohydrides.
Grassberger et al., Angew. Chem. Int. Ed. 8: 275 (1969), disclose a process for preparing alkali-metal tetraorganylborates by reacting alkali-metal tetraethylborates and triorganylboranes at 130.degree.-180.degree. C., e.g., EQU 3MB(C.sub.2 H.sub.5).sub.4 +4BR.sub.3 .revreaction.3MBR.sub.4 +4B(C.sub.2 H.sub.5).sub.3.
M in the foregoing formula is Na or Li; R is a butyloxy, allyloxy, carbyl, methallyl, phenyl, benzyl or pyrrolyl group.
The availability of certain tetraorganyl compounds has been limited by the lack of a direct, efficient, convenient process for their synthesis. Certain methods representative of the prior art are complex, requiring use of gaseous reactants or extensive purification procedures to make tetraorganylborate compounds of a grade suitable for quantitative analysis.